Comment by geor9e

Because the USB Consortium made a terrible mistake. Instead of speccing USB-PD power supplies to default to 5V <3A when there are no resistors in the port of the other device, the default is do nothing. So in order to be in spec, you have to refuse to charge non-compliant ports. This means the compliant power supplies are worse, in a way. So you need to use a "dumb" USB-A power supply and USB-A to C cable, which does default to 5V <3A to matter what. As for why some devices choose to use non-compliant ports - I assume it's extreme cheapness. They save a penny on a resistor.